Conventional solar control films are generally made by metallizing a thin layer of aluminum metal on polymeric film substrates, usually polyester (PET) and laminating it with a second colored PET film. The films are installed on an interior surface of window glasses. The product is designed to fulfill needs of solar energy control permitting required visible light transmittance. The acceptable limits of Visible Light Transmittance (VLT) and Reflectance in desired colors is achieved by combination of colored films and aluminum metallized films.
Commercially available films are with VLT ranging from 3% to 70%. The window film laminate consists of optically clear, distortion free PET film with thickness of 23 microns (μ) to 300μ coated with acrylic base pressure sensitive adhesive and protected with a release liner.
The colors and ultraviolet (UV) stabilizers are incorporated in the polymer matrix. The design of the product allows optimum control of the electromagnetic spectrum passing through the window glasses of automobiles and buildings. UV portion of electromagnetic spectrum is absorbed by UV absorbers incorporated in the polymer matrix and pressure sensitive adhesive. Visible light is controlled by appropriate combination of Blue, Red & Yellow absorbing materials incorporated in the PET film. These films have low haze and high clarity. However, prolonged exposure to natural weather conditions lead to fading of the film.
As yellow is more prone to fading, UV stabilizers, heat stabilizers, hindered amine stabilizers are added to minimize the rate of decomposition though the degradation cannot be completely stopped. There is a need to improve fading property of dyed window film laminates when exposed to prolonged natural exposure conditions by maintaining high clarity standards and one tone fading property.
Alternative method to make tinted PET films is to add organic pigments, organic metal complexes in pressure sensitive adhesives or to apply pigmented coatings on the surface of PET films. These films have severe performance drawbacks as long-term exposure of these coatings to natural weather conditions causes progressive fading and transmittance loss.
Visible light reflectance of the aluminum metallized films has been minimized by combining reflective films with dyed films. Metallized part of the film is generally kept on the outer side whereas the part of the film with the dyed part is kept on the inner side. Despite this arrangement, the dyed portion of the film used fades faster as compared to the metallized portion.
The various methods have been investigated in U.S. Pat. No. 6,294,251, U.S. Pat. No. 5,512,215, U.S. Pat. No. 5,518,810, U.S. Pat. No. 6,191,884 and U.S. Pat. No. 6,404,543 and references therein, to attend the desired level of aesthetics, optics and solar energy rejection properties of laminated window glazing, which includes treating of polymeric films using chemical vapor deposition, sputtering of metals, oxides, thermal vacuum deposition of metals, the coloring of the polymeric films and the combination of metal coated films and dyed films.
U.S. Pat. No. 4,430,366 describes a process for aluminum (Al) oxide deposition on polymeric films. Metal oxide layer is formed in continuous vacuum deposition process. The reactive materials like oxygen, hydrogen sulfide are introduced in metal vapor stream under vacuum using conventional metal deposition apparatus. These films have less moisture vapor transmittance rate and needs longer drying time when installed on window pans. In other approaches, reflective aluminum metal films are sandwich between two dyed films. Al looses it's reflectivity by reacting with surface impurities on the dyed film and glycol traces within the polymer matrices of the colored films and therefore Al metallizing on the dyed film have not been commercially successful. Further metallized films have higher visible light reflectance, which is not desirable. The production of such films also entails higher cost of production.
U.S. Pat. No. 6,833,184 describes window films wherein coloration of the window film is affected by a pigment having small particle size that are coated with a resin binder, which encapsulates the organic pigment particles. The adhesive with the encapsulated organic pigment particles is used to secure one or more film layers of a composite window film structure together. Organic dyes have several limitations as they have low inferior light and weather resistance as compared to inorganic pigments and ceramic materials.
U.S. Pat. No. 6,569,517 in contrast to the others has disclosed a color-tailorable surface-metallized, pigment optical body comprising a single or multiple layer polymeric core comprising at least one layer of a thermoplastic polymer material having dispersed therein a particulate pigment, and a metallic layer located on at least one outer surface of the polymeric core. It may be noted in the invention disclosed in U.S. Pat. No. 6,569,517 that the particulate pigment such as carbon black, diverse metal oxides, sulphides, selinides, silicates, manganates, etc., is to be necessarily dispersed in the single or multiple core polymeric layer. Production of such polymer core layers is commercially unattractive. The process needs several controls and becomes expensive.
U.S. Patent Application Publication No. 2004/0131845 A1 discloses a heat wave shielding resin sheet which has maximum transmittance in the visible light region and at the same time minimum transmittance in the near-infrared region exhibiting strong absorption and is realized by dispersing rare earth hexaboride fine particles such as lanthanum hexaboride (LaB6) as a heat wave shielding component in polycarbonate resin or acrylic resin. Indium containing tin oxide (ITO) fine particles and/or antimony containing tin oxide (ATO) fine particles can be dispersed together with the rare earth hexaboride fine particles.
U.S. Pat. No. 6,319,613 describes a solution for forming a film having a high transmittance and a low reflectivity for visible light, a low transmittance for near infrared radiation, and a surface resistively of at least 106 ohms/square. It contains fine particles of a hexaboride of Yttrium (Y), Lanthanum (La), Cerium (Ce), etc., Strontium (Sr), or Calcium (Ca) and fine particles of ITO or ATO in a weight ratio of from 0.1:99.9 to 90:10. In addition to the hexaboride and ITO or ATO, the solution may contain additional fine particles of at least one oxide selected from the group consisting of silicon dioxide (SiO2), titanium dioxide (TiO2), zirconium dioxide (ZrO2), aluminum oxide (Al2O3) and magnesium oxide (MgO) with particle diameters up to 200μ. Also disclosed is a film formed on at least one-side of a resin film as a base for cutting off solar heat radiation. Higher concentration of nano material is required to put in coating to make the films having darker tints therefore it is very expensive and is not economical. This technique is used to make the film with visible light transmittance above 60 percent (%).
U.S. Pat. No. 6,953,618 describes a method for achieving predetermined finished colour tone of window film laminate comprising the transparent colour film having colour deficiency in hue, chroma and at least one pigment dispersed in transparent colour matching layer adjacent to film layer, wherein the pigment is iron oxide.
U.S. Pat. No. 6,404,543 describes an infrared (IR) shielding film having excellent visible light transmission and near IR blocking properties. The infrared shielding films are prepared by applying a thin coating layer consisting of ionizing radiation curable resin and Lanthanum as near infrared shielding agent. Xenon Arc Weatherometer exposure results shows that the infrared shielding nano composites are sensitive to humidity, progressively losing near infrared ray blocking property.
U.S. Pat. No. 6,294,251 discloses a method for making colored film where an adhesive is colored with pigments being applied on at least one side surface of transparent film. These films have the severe drawback that when exposed to natural weather conditions they progressively lose visible light transmittance and fade.
The present invention relates to multi layered polyester films with sandwiched adhesive layer with dispersed fine mixed metal oxides as solar-energy-screen particles such as complex oxides of copper and manganese, optionally in combination with hexaborides such as LaB6, and/or ATO, ITO, titanium nitride (TiN) fine particles to give a good tinting strength. The present invention further provides a cost effective process for the manufacture of the product.